Retroreflective materials, i.e., those which reflect a predominant portion of the light incident thereon substantially parallel to the incident light back toward the source, are commonly used for safety purposes in highway markers, vehicle reflectors, and the like. In such retroreflective materials comprising a multiplicity of cube corners, the orthogonality of the faces forming the cube corners must be maintained precisely or the retroreflective properties are greatly diminished. It is possible to control advantageously the angular divergence of the retroreflected light by varying the interface dihedral angles of the cube corners, but random distortion thereof generally results in unwanted loss of brightness.
An object of U.S. Pat. No. 3,684,348 for "Retroreflective Material," granted Aug. 15, 1972, was to provide a flexible retroreflective sheet material utilizing cube corners which would conform and adhere to non-planar support surfaces. While this retroreflective material has functioned very well, it has been found that, if stretched during application to a support surface, such as wrapping a tape made therefrom helically around bicycle handlebars, the cube corners are distorted. This renders the cube corner faces non-orthogonal to a degree resulting in significant loss of brightness.
Accordingly, it is an object of the present invention to provide a novel strechable retroreflective sheet material utilizing cube corner retroreflectors which is easily applied under tension to support surfaces and provides good retroreflection when stretched a predetermined amount.
It is also an object to provide such retroreflective material with a high friction or adhesive coating by which it may be conveniently held against slippage on a support surface.
Another object is to provide such retroreflective material wherein the tension used to stretch the material about the support surface while avoiding distortions of the cube corner formations is readily determined during application to the support surface.
Still another object is to provide a novel method for manufacturing such retroreflective material which is relatively simple and economical and which facilitates the establishment of a visual gauge for the stretching tension desired during application thereof to a support surface.